An image printing method employing ink-jet systems is one in which minute ink droplets are ejected from an ink-jet recording head and deposited onto recording media to be printed. Ink-jet recording systems feature a mechanism which is relatively simple and low in cost, and also enables forming highly detailed images of high quality.
Taking advantages of such ink-jet recording systems, image printing onto textiles, so-called ink-jet textile printing, has been developed. Differing from conventional textile printing, ink-jet textile printing exhibits advantages which makes it possible to quickly form images of excellent gradation without need of plate making. Further, since only the amount of ink which is necessary is used to form images, the ink-jet textile printing is considered as an excellent image forming method to minimize environmental pollution due to its minimal effluent.
In ink-jet textile printing, the types of usable dyes are limited depending on the kinds of fibers constituting textile, and disperse dyes are commonly employed for dying polyester based fibers.
There are various types of ink-jet recording systems include. On-demand type recording systems, which are the main stream in recent years, are divided into a so-called piezo system (a piezoelectric system) employing a piezo element, and a thermal ink-jet system (the BABBLE JET (a registered trade name) system). Of these, in the ink-jet recording system employing the piezo system, it has been known that since decrease and increase in pressure are repeated innumerable times during ink ejection, tiny air bubbles tend to form due to cavitation, resulting in absence of dots during ink ejection and shifting ink deposition position, whereby degradation of print quality such as graininess occurs.
Generally, cavitation, as described herein, refers to the physical phenomenon in which when the pressure of a liquid at a certain temperature becomes lower than the vapor pressure to be exhibited at the above temperature, the liquid evaporates, forming bubbles. On account of that, ink-jet ink to be employed is generally degassed to minimize gas content in the ink-jet ink, whereby generation of air bubbles during ejection is minimized. Degassing is performed employing, for example, a method in which an ink-jet ink is degassed under reduced pressure, a method in which ultrasonic waves are applied to an ink-jet ink for degassing, and a method in which a degassing hollow fiber membrane is used, as described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) No. 11-209670. Further, an ink-jet printer is proposed which incorporates a device capable of continuously practicing an ultrasonic degassing method and a hollow fiber degassing method. Still further, though a physical method is not employed, JP-A No. 11-263929 proposes a method in which formation of air bubbles are minimized employing surface active agents.
Any of the methods proposed above exhibit some preferred effects for soluble type ink-jet inks. However, in the dispersion system in which pigments and disperse dyes which are barely soluble or insoluble in water are employed, it is difficult to achieve stable ejection while simultaneously minimizing the generation of cavitation. Further, when an ultrasonic degassing device or a hollow fiber membrane degassing device is incorporated in an ink-jet printer, it is necessary to install each of such degassing devices for each of the ink-jet series of each color. As a result, a relatively enormous amount of space is required, whereby the size of the ink-jet printer increases, resulting in an inevitable increase in device production cost. Consequently, the above methods are not regarded as efficient ones. In addition, problems are included in which when these devices malfunction, it makes the ink-jet printer inoperable. Still further, when these devices are not used for an extended period of time, problems occur in which coagula are generated in the ink cartridge or prior to reaching the degassing device due to the gas incorporated in the ink-jet ink.
On the other hand, disclosed is a processing method (refer, for example, to Patent Document 1) of a recording liquid, which decreases fluctuation of the amount of ejected ink by performing an ultrasonic degassing treatment or a vacuum degassing treatment after preparing an aqueous pigment based recording liquid composing dispersing agents, water-soluble media, pigments and water. However, the above disclosed method aims at improving dispersibility of pigment particles or enhancing the uniformity of the particle size distribution by removing air absorbed on the surface of pigment particles, and further increasing mutual interaction with dispersing agents via simultaneously performing an ultrasonic treatment and a vacuum degassing treatment, but does not aim at improving cavitation in the ink-jet ink. Further, neither description nor suggestion is made in regard to the minimization of generation of cavitation in cases in which disperse dyes are specifically employed as a colorant.
Further, proposed is a method (refer, for example, to Patent Document 2) in which dispersibility of pigments is enhanced by peptizing the secondary coagula of pigment particles, formed during preparation of concentrated colorant dispersion, which is prepared by applying ultrasonic wave energy to a highly concentrated colorant dispersion at during preparation of ink. However, the above disclosed method aims to re-disperse coagulated pigment particles into the primary particles, employing ultrasonic wave energy, and does not intend to improve cavitation in the ink-jet ink. Further, neither description nor suggestion is made in regard to prevention of the formation of cavitation under specifically use of disperse dyes as a colorant.
As noted above, the present situation is one in which a dispersion based ink-jet ink has not yet been attained which simultaneously satisfies stable ejection and cost as desired.
(Patent Document 1) JP-A No. 9-286943 (claims)
(Patent Document 2) JP-A No. 11-228892 (claims)